Method of making delamination resistant composites

ABSTRACT

Fiber reinforced resin composites formed by elements joined by a high shear strength, high fracture toughness adhesive are disclosed. The elements are created in easily produceable cross-sectional shapes such as flat, C-shaped, Z-shaped or T-shaped. When joined, the elements form delamination resistant fiber reinforced resin composites having more complex shapes. The strength of the junctions between a pair of elements, such as a panel and its associated reinforcing members, can be enhanced by fasteners, such as rivets, if desired.

TECHNICAL AREA

This invention relates to fiber reinforced resin composites and, moreparticulary, delamination resistant fiber reinforced resin composites.

BACKGROUND OF THE INVENTION

In recent years the use of high strength-to-weight ratio fiberreinforced resin composites has continuously expanded, particulary inweight sensitive products, such as aircraft and space vehicles. Fiberreinforced resin composites are usually formed by "laying-up" aplurality of plies formed of reinforcing fibers. The plies may bepreimpregnated with resin; or, resin layers may be added to stacks ofdry plies as the lay-up is being formed. In any event, after a lay-up isformed, the resin is cured by applying heat and, usually, pressure tothe lay-up. When dry plies and resin layers form the lay-up, the resinis infused into the dry plies as it is cured. In the past, a widevariety of fiber reinforced resin composite components, such as panels,reinforcing members and combinations thereof, have been formed in thismanner.

As the use of fiber reinforced resin composites has expanded, the desireto maintain weight at a minimum commensurate with structural integrityhas increased the complexity of the resulting structures. In the past,complex structures have been either laid up and cured as a single itemor separately formed and joined by mechanical fasteners, such as rivets.Both of these approaches have disadvantages. Complex structures have thedisadvantage that they are difficult to layup. Using mechanicalfasteners to join previously created fiber reinforced resin compositereinforcing members and panels has the disadvantage of creating jointsthat tend to weaken as vibration causes wear about the periphery of theholes in which the fasteners are mounted.

As the complexity of fiber reinforced resin composites has increasedother problems have also developed. These problems are primarily aresult of the ply by ply nature of resin composites, which makes themsusceptible to delaminate along interlaminar planes. The tendency todelaminate is, of course, a result of the fact that most composites donot have fibers in the through thickness direction (i.e., the directionorthogonal to the planes of the plies that form the composite), wherebyall resistance to delamination along interlaminar planes is a functionof the properties of the resin, which usually has a strength 50 to 100times less than the ply fibers, or a comparable substitute metal.

Several attempts have been made to solve the delamination problem notedabove. One attempt involves modification of the chemistry of the resinsused in fiber reinforced resin composites to increase resin fracturetoughness while maintaining composite compression strength. Most methodsof increasing the fracture toughness of a brittle resin, such as anepoxy, involve the addition of at least one component with a lower shearmodulus than the resin base. The disadvantage of this approach is thatthis addition results in a drop of the overall shear modulus. Inenvironments where this approach has been tried, namely in connectionwith the manufacture of components for aircraft and space vehicles, theshear modulus has dropped below that required to maintain compositecompression performance. This approach also has the disadvantage ofincreasing the susceptibility of the resultant fiber reinforced resincomposite to heat and solvents.

A further approach to solving the tendency of fiber reinforced resincomposites to delaminate has been to add more mass to keep stressesbelow the maximum dictated by a low delamination resistance. Thisapproach has the disadvantage of substantially reducing the weightsaving advantages of fiber reinforced resin composites.

Another approach used to solve the delamination problem is to designdiscrete portions of a composite to have a substantially higherstiffness than the remainder of the composite. The stiffener portionsbecome the primary load carrying paths and can be varied to meetstructural requirements. The disadvantage of this approach is that itplaces severe restrictions on design. Further, weight is increased bythe material added to discretize the stiffness of various load paths.The end result is a structure that is heavier and more difficult tomanufacture than comparable structures that do not have these designconstraints.

Finally, the delamination resistance of fiber reinforced resincomposites along interlaminar planes has been improved by cross-plystitching laminate plies together. While this approach does notsubstantially increase the weight of the resultant reinforced resincomposite, it is difficult to satisfactorily implement in fiber resinreinforced composites having complicated cross-sectional configurations.

The present invention is directed to delamination resistant fiberreinforced resin composites that avoid the disadvantages describedabove.

SUMMARY OF THE INVENTION

In accordance with this invention, fiber reinforced resin compositesformed of elements joined by a high shear strength, high fracturetoughness adhesive are provided. The elements have any easilyproduceable cross-sectional shapes such as flat, C-shaped, Z-shaped andT-shaped. When joined the elements form fiber reinforced resincomposites having more complicated cross-sectional shapes.

In accordance with further aspects of this invention, the strength ofthe junctions between elements, such as a panel and reinforcing membersare enhanced by mechanical fasteners, such as rivets.

One particular form of the invention comprises pairs of elongate fiberreinforced resin composite elements having C-shaped cross-sectionalconfigurations. The backs of the C-shaped elements are joined by a layerof high shear strength adhesive. The flanges on one side of theresulting I-shaped reinforcing member is attached to a fiber reinforcedresin composite panel by another layer of high shear strength adhesive.If desired, the stiffness of the flanges on the other side of theI-shaped reinforcing member can be increased by attaching a fiberreinforced resin composite flat plate to the other flanges by a furtherlayer of high shear strength, fracture tough adhesive. Also if desired,the strength of the junction between the panel supporting flanges of theI-shaped reinforcing members and the panel can be increased by addingmechanical fasteners, such as rivets.

An alternative form of a fiber reinforced resin composite reinforcingmember formed in accordance with the invention is created by firstlongitudinally slicing one edge of an elongate relatively thick, flatfiber reinforced resin composite plate to create two equal thicknesssegments. The segments are bent outwardly to create a flange, which isattached to a panel to be supported by a layer of high shear strengthadhesive. If desired, the edge of the flat plate opposed to the edgeforming the flanges can be bent outwardly to stiffen the leg of thethusly formed, generally T-shaped, reinforcing member.

As will be readily appreciated from the foregoing brief summary, theinvention provides fiber reinforced resin composites that overcome thedisadvantages of prior fiber reinforced resin composites discussedabove. Because fiber reinforced resin composites formed in accordancewith the invention are created from elements having easily produceableshapes, the plies forming such elements can be readily laid up andcross-ply stitched. Further, because the elements are joined by layersof high shear strength, tough adhesive, the possibility of delaminationat the interface between the elements is substantially reduced from whatit would be if the elements were merely joined by a low fracturetoughness, low shear strength resin of the type used to create the fiberreinforced resin composite elements.

BRIEF DESCRIPTION OF THE DRAWINGS

The foregoing objects and many of the attendant advantages of thisinvention will become more readily appreciated as the same becomesbetter understood by reference to the following detailed descriptionwhen taken in conjunction with the accompanying drawings wherein:

FIG. 1 is a perspective view of a delamination resistant fiberreinforced resin composite formed in accordance with the invention;

FIG. 2 is a perspective view of the delamination resistant fiberreinforced resin composite illustrated in FIG. 1 with the addition ofmechanical fasteners;

FIG. 3 is a perspective view of an alternative embodiment of adelamination resistant fiber reinforced resin composite formed inaccordance with the invention;

FIG. 4 is a sequence of views illustrating the formation of thereinforcing member forming part of the delamination resistant fiberreinforced resin composite illustrated in FIG. 3;

FIG. 5 is a perspective view of another embodiment of a delaminationresistant fiber reinforced resin composite formed in accordance with theinvention;

FIG. 6 is a perspective view of a further embodiment of a delaminationresistant fiber reinforced resin composite formed in accordance with theinvention:

FIG. 7 is a perspective view of the delamination resistant fiberreinforced resin composite illustrated in FIG. 6 with the addition ofmechanical fasteners;

FIG. 8 is a perspective view of yet another embodiment of a delaminationresistant fiber reinforced resin composite formed in accordance with theinvention;

FIG. 9 is a perspective view of yet still another embodiment of adelamination resistant fiber reinforced resin composite formed inaccordance with the invention; and,

FIG. 10 is a perspective view of a still further embodiment of adelamination resistant fiber reinforced resin composite formed inaccordance with the invention.

DESCRIPTION OF THE PREFERRED EMBODIMENTS

FIG. 1 is a perspective view of a delamination resistant fiberreinforced resin composite formed in accordance with the invention andcomprises a panel 11 and a plurality of parallel oriented I-shapedreinforcing members 13. The panel 11 is formed of a plurality of fiberplies 12 laid up in a conventional manner. The plies 12 may originate asprepreg plies (i.e., plies preimpregnated with resin) or dry pliescombined with one or more layers or sheets of resin tiles. In any event,the delamination resistance of the plies is enhanced by cross-plystitches 14.

Each of the I-shaped reinforcing members 13 is formed of two C-shapedelements 15A and 15B and a flat stiffening plate 17. Each of theC-shaped reinforcing elements 15A and 15B is formed of a plurality oflaid up plies 19 held together by a suitable resin. As with the panel11, the plies may originate as prepreg plies or dry plies combined witha layer or layers of resin. In any event, the delamination resistance ofthe plies is enhanced by cross-ply stitches 20. The flat stiffeningplate 17 is also formed by a plurality of laid up plies 21 held togetherby a suitable resin that has enhanced delamination resistance as aresult of cross-ply stitches 22.

The C-shaped elements 15A and 15B are positioned back to back and joinedby a first layer of high shear strength, high fracture toughnessadhesive 23, which is more fully described below. The result is areinforcing member having an I-shaped cross sectional configuration. Theplate 17 is aligned with the outer face of the flanges located on oneside of the I-shaped reinforcing member and is attached thereto by asecond layer of high shear strength, high toughness adhesive 25.

The reinforcing members 13 are positioned in parallel on one side of thepanel 11 such that the outer faces of the flanges of the I-shapedreinforcing members remote from the flanges attached to the plate 17face the panel 11. The panel facing flanges of the I-shaped reinforcingmembers 13 are attached to the panel by third high shear strength, hightoughness adhesive layer 27.

The final configuration of the fiber reinforced resin compositeillustrated in FIG. 1 can be formed and cured in various ways. Ifdesired, the two C-shaped elements 15A and 15B, the flat stiffeningplate 17 and the panel can all be individually laid up and cured inaccordance with prior art procedures. The cured elements and the firstand second high shear strength, high toughness adhesive layers 23 and 25can be assembled in the manner described above. After the assemblies areformed, the first and second high shear strength, high toughnessadhesive layers 23 and 25 can be cured to create fully cured reinforcingmembers 13. Thereafter, the reinforcing elements 13 and the panel 11plus the third high shear strength, high toughness adhesive layer can beassembled in the manner illustrated in FIG. 1 and previously described;and then, the third high shear strength, high toughness adhesive layer27 cured.

An alternative to the steps just described is to form the elements ofthe reinforcing members, assemble them with the first and second highshear strength, high toughness adhesive layers 23 and 25 andsimultaneously cure the entire assembly, i.e., cure the first and secondhigh shear strength, high toughness layers at the same time the resinmatrix that holds the fibers together is cured. A further alternative toassemble the entire structure illustrated in FIG. 1, i.e., all of theelements of the reinforcing members 13 and the panel 11, plus all threehigh shear strength, high toughness adhesive layers 23, 25 and 27, andcure the entire assembly at the same time.

FIG. 2 illustrates a delamination resistant fiber reinforced resincomposite identical to the delamination resistant fiber reinforced resincomposite illustrated in FIG. 1 to which a plurality of mechanicalfasteners 29 have been added. The mechanical fasteners 29 extend throughthe panel 11 and juxtaposed flanges of the reinforcing members 13. Thus,the fasteners 29 extend through and enhance the delamination resistanceof the fiber reinforced resin composite in the area of the third highshear strength, high toughness adhesive layer 27. While illustrated assolid rivets, it is to be understood that other types of fasteners canbe used such as hollow rivets, nuts and bolts, etc., depending upon whatis acceptable in a particular environment.

As will be readily appreciated by those familar with composites,normally, the use of fasteners to join fiber reinforced resin compositemembers together is unacceptable, particulary in high vibrationenvironments, because flexing of the members due to vibration wears awaythe composite material around the periphery of the holes in which thefasteners are mounted. The inclusion of the third high shear strength,high toughness adhesive layer 27 substantially reduces this undesirableresult because the vibration flexing of the members at the junctionbetween the panel 11 and the reinforcing members 13 is substantiallyreduced by the third high shear strength, high toughness adhesive layer.Further, flow of the adhesive around the fasteners 29 provides a bondbetween the fasteners and the members joined by the fasteners if theadhesive is cured after the holes have been drilled and the fastenersinserted. Maximum join strength is attained by applying pull up torqueto a threaded fastener, if used, or heading a rivet, if used, after theadhesive has been cured.

FIG. 3 illustrates a delamination resistant fiber reinforced resincomposite formed in accordance with the invention that comprises a panel31 stiffened and supported by a plurality of elongate, generallyt-shaped, reinforcing members 33. Both the panel 31 and the reinforcingmembers are formed of a plurality of laid-up plies. The delaminationresistance of the ply lay-ups is enhanced by cross-ply stitching. Also,preferably, the generally t-shaped reinforcing members 33 are formed inthe manner illustrated in FIG. 4 and described below. The generallyt-shaped reinforcing members 33 lie along parallel axes and are attachedto the panel 31 via their flanges by a high shear strength, highfracture toughness adhesive layer 39. As before, the high shearstrength, high fracture toughness adhesive layer can be cured at thesame time the resin that binds the plies together is cured or thereinforcing members 33 and the panel 31 can be created separately andtheir resins cured prior to being joined by the high shear strength,high touchness adhesive layer 39.

FIG. 4 is a sequence of views illustrating the preferred way of formingthe generally t-shaped reinforcing members illustrated in FIG. 3. First,a stack of plies 41 are laid up. Since the reinforcing members areelongate, in essence, the result is an elongate stack of plies. A slit43 is then made along one edge of the stack of plies 41. Preferably, thenumber of plies lying on either side of the slit is identical. Thethusly separated plies are then bent outwardly to form a pair of flanges45 that lie orthogonal to the remainder of the structure. At this point,the structure has a cross-sectional shape of a T. Next, the edge of thestack of plies 41 remote from the flanges 45 (i.e., the leg of the T) isbent to form a protrusion 47 that lies parallel to one of the flanges45. After being thusly formed, the resin of the now generally t-shapedsupport member is cured either prior to attachment to the panel 31 (FIG.3) by the high shear strength, high toughness adhesive layer 39 or afterattachment, as previously described.

FIG. 5 is a perspective view of a further embodiment of a fiberreinforced resin composite formed in accordance with the inventioncomprising a panel 51 reinforced and supported by a plurality ofelongate, parallel oriented reinforcing members 53. While thereinforcing members 53 have the same cross-sectional configuration asthe generally t-shaped reinforcing members 33 illustrated in FIG. 3,they are formed in a different manner. Specifically, the reinforcingmembers 53 illustrated in FIG. 5 are each formed of two elements--aZ-shaped element 55 and a C-shaped element 57. As with the previouslydescribed embodiments of the invention, the Z-shaped elements 55 and theC-shaped elements 57 are formed by laying up a plurality of plies joinedby a resin matrix. The plies may be prepreg plies or dry plies to whichone or more layers of resin are added, the resin being infused into thedry plies during curing as described in U.S. patent application Ser. No.676,427, filed Nov. 29, 1984, by Leslie E. Letterman and entitled "ResinFilm Infusion Process and Apparatus". As illustrated, the plies of boththe panel 51 and the reinforcing members 53 are cross-ply stitched toimprove delamination resistance.

The reinforcing members are created by positioning the C-shaped elements57 such that the back of a C-shaped element faces one side of the centerleg of a Z-shaped element 55 and the outer surface of one of the legs ofthe C-shaped element 57 faces the inner surface of one of the legs ofthe Z-shaped element 55. Located between facing surfaces of the Z-shapedelement 55 and the C-shaped element 57 are first and second high shearstrength, high fracture toughness adhesive layers 59 and 61. A thirdhigh shear strength, high toughness adhesive layer 63 is located betweenthe panel 51 and the flanges of the thusly formed generally t-shapedreinforcing member 53. As before, the Z-shaped and C-shaped elements 55and 57 that form the reinforcing members 53 can be separately formed andcured or the elements can be joined by the first and second high shearstrength, high toughness adhesive layers 59 and 61 before the C-shapedand Z-shaped elements are cured; or the entire fiber reinforced resincomposite structure illustrated in FIG. 5 can be assembled prior toresin and adhesive curing.

FIG. 6 illustrates a fiber reinforced resin composite formed inaccordance with the invention that comprises a panel 71 supported andreinforced by a plurality of elongate, generally t-shaped reinforcingmembers 73. The difference between the fiber reinforced resin compositeillustrated in FIG. 6 and the fiber reinforced resin compositeillustrated in FIGS. 3 and 5 resides in the way the generally t-shapedreinforcing members are formed. Rather than being formed of a singleelement or two elements, i.e., a Z-shaped element and a C-shapedelement, the generally t-shaped reinforcing members 73 illustrated inFIG. 6 are each formed of three elements--a Z-shaped element 75; aC-shaped 77; and, a flat plate 79.

The flat plate 79 is positioned in the corner created by the center leg81 and one of the outer legs 83 of the Z-shaped element 75. A firstlayer of high shear strength, high toughness adhesive 85 is positionedbetween the facing surfaces of the flat plate 79 and the outer leg 83 ofthe Z-shaped element 75. A second layer of high shear strength, hightoughness adhesive 87 is located between the edge of the flat plate 79and the facing area of the center leg 81 of the Z-shaped element 75. TheC-shaped element 77 is positioned in the corner created by the othersurface of the flat plate 79 and the center leg 81 of the Z-shapedelement 75. The orientation of the C-shaped element is such that theouter surface of one leg 89 of the C-shaped element faces the othersurface of the plate 79 and is attached thereto by a third layer of highshear strength, high toughness adhesive 91. The back of the C-shapedelement 77 faces the center leg 81 of the Z-shaped element 55 and isattached thereto by a fourth layer of high shear strength, hightoughness adhesive 93. The C-shaped element 77 is sized such that theouter surface of its other leg 95 is co-planar with the outer surface ofthe other outer leg 97 of the Z-shaped element 75. The outer surface ofthe outer leg 95 of the C-shaped element 77 and the other outer leg 97of the Z-shaped element 75 are attached to the panel 71 by a fifth layerof high shear strength, high toughness adhesive 99.

As with the previously described embodiments of the invention, theindividual elements that form the fiber reinforced resin compositeillustrated in FIG. 6 can be formed and cured separately prior to beingjoined together. Or some of the elements, such as all of the elementsthat form the elongate, generally t-shaped reinforcing members 73, canbe cured after being joined. Or, still further, all of the elements,including the panel 71, can be joined and the resin and adhesive layersof the entire three dimensional fiber reinforced resin compositesimultaneously cured. In addition, the various high shear strength, hightoughness layers 85, 87, 91, 93 and 99 can be butt spliced where theymeet, i.e., it is not necessary that the second and third layersoverlap, for example.

FIG. 7 illustrates a three dimensional fiber reinforced resin compositeformed in accordance with the invention identical to the threedimensional fiber reinforced resin composite illustrated in FIG. 6 andpreviously described to which a plurality of mechanical fasteners 101have been added. The mechanical fasteners lie in holes that extendthrough the panel 71 and the juxtaposed flanges 95 and 97 of theelongate, generally t-shaped support members 73. While the mechanicalfasteners 101 are illustrated as rivets, it is to be understood thatother types of fasteners can be utilized, if desired.

FIG. 8 illustrates a three dimensional fiber reinforced resin compositeformed in accordance with the invention that comprises a panel 111supported and stiffened by a plurality of elongate, parallel orientedZ-shaped reinforcing members 113. As with the previously describedembodiments of the invention, the panel and the Z-shaped reinforcingmembers 113 are each formed of a plurality of fiber reinforcing pliesheld together by a resin matrix. The plies can be cross-ply stitched asillustrated by the dashed lines. Rather than being formed of a pluralityof elements joined by high shear strength, high fracture toughnessadhesive layers, the Z-shaped reinforcing members 113 of the fiberreinforced resin composite illustrated in FIG. 8 are a single element.One of the legs 115 of each Z-shaped reinforcing member 113 underliesthe panel 111 and is joined thereto by a layer of high shear strength,high toughness adhesive 117. As with the previously describedembodiments of the invention, the panel 111 and the Z-shaped reinforcingmembers 113 can be formed and cured as separate items prior to beingjoined together by the high shear strength, high toughness adhesivelayers 117. Alternatively, the panel 111 and the Z-shaped reinforcingmember 113 resins can be cured simultaneously with the curing of thehigh shear strength, high toughness adhesive layers 117.

FIG. 9 illustrates a further alternative embodiment of a fiberreinforced resin composite formed in accordance with the invention. Theembodiment of the invention illustrated in FIG. 9 includes a panel 121supported and stiffened by a plurality of parallel oriented, elongatehat-shaped reinforcing members 123. The hat-shaped reinforcing members123 are formed from a plurality of laid up fiber reinforcing plies heldtogether by a resin matrix. As in the previously described embodimentsof the invention, preferably, the plies are stitched in a cross-plydirection to increase delamination resistance. As illustrated in FIG. 9,depending upon design and other criteria, either the cross member of thehat-shaped reinforcing elements 123 can be attached to the panel 121 bya single layer of high shear strength, high toughness adhesive 127 orthe flanges can be attached by two layers of high shear strength, hightoughness adhesive 129. Obviously, if desired, the same region of allhat-shaped reinforcing elements can be attached to the panel 121 in thesame way, rather than some being attached one way and others beingattached the other way, as illustrated in FIG. 9.

As with the previously described embodiments of the invention, the panel121 and the hat-shaped reinforcing members 123 illustrated in FIG. 9 canbe separately formed and cured prior to being joined, or they can bejoined and their resins cured simultaneously with the curing of the highshear strength, high toughness adhesive layers. In addition, fastenerscan be applied at the junction between the hat-shaped reinforcingmembers 123 and the panel 121.

FIG. 10 is a perspective view of yet still another three dimensionalfiber reinforced resin composite formed in accordance with theinvention. The fiber reinforced resin composite illustrated in FIG. 10comprises a panel 131 supported by a plurality of elongate, wideU-shaped reinforcing members 133. As with the previously describedembodiments of the invention, the panel 131 is formed of a stack ofplies 135 held together by a resin matrix. The plies can be stitchedtogether in the cross-ply direction to improve delamination resistance.The wide U-shaped reinforcing members 133 include a wide cross leg 137facing one side of the panel 131. The U-shaped support members are alsoformed of a plurality of plies 145 held together by a resin matrix. Thedelamination resistance of the U-shaped reinforcing members 137 can beenhanced by cross-ply stitching. The wide U-shaped reinforcing members133 are sized such that the legs of adjacent U-shaped support andreinforcement members can be attached together by a first layer of highshear strength, high fracture toughness adhesive 141. A second layer ofhigh shear strength, high toughness adhesive 143 attaches the cross legs137 of the wide U-shaped support reinforcing members 133 to thejuxtaposed face of the panel 131.

As with the previously described embodiments of the invention, the wideU-shaped reinforcing members 133 and the panel 131 can be separatelyformed and cured prior to being joined by the first and second highshear strength, high toughness adhesive layers 141 and 143.Alternatively, the panel 131 and the wide U-shaped reinforcing members133 can be laid up and joined by the high shear strength, high toughnessadhesive layers prior to their resin being cured. In the latter case,the high shear strength, high fracture toughness adhesive layers 141 and143 are cured simultaneously with the curing of the panel 131 and thewide U-shaped support and reinforcing member resins.

As will be readily appreciated from the foregoing description, theinvention comprises three dimensional fiber reinforced resin compositesformed of elements joined by high shear strength, high fracturetoughness adhesive layers. The elements are in easily reproduceableconfigurations, such as flat, C-shaped, Z-shaped or T-shaped, as opposedto being in more complex configurations. In accordance with theinvention, the elements can be joined to form complex reinforcing memberconfigurations and combined with panels to create relatively complicatedfiber reinforced resin composites. Because the elements are joined byhigh shear strength, high toughness adhesive layers, fiber reinforcedresin composites formed in accordance with the invention have a higherresistance to delamination than they would have if the elements werejoined by a resin of the type utilized to hold individual fiber pliestogether.

As will be readily appreciated from the foregoing description, the highshear strength, high fracture toughness adhesive used to formembodiments of the invention is not the same as the resin infused intothe fiber plies of the various elements and members to bind the pliestogether. Rather the adhesive has considerably higher shear strength,which is what makes it more split resistant. One adhesive that isideally suited for use in creating embodiments of the invention for usein aircraft is the FM300 thermosetting adhesive film available fromAmerican Cynamid Company, Bloomingdale Department, Harve de Grace, Md.21078. The double lap shear strength of this adhesive is approximately3000 PSI at room temperature. Its room temperature (75°±5° F.) honeycombflatwise tensile strength and its sandwich beam shear strength are bothbetter than 500 PSI. Other thermosetting adhesives suitable for use inthis invention are the AF147 adhesive manufactured by the 3M Company, 3MCenter, St. Paul, Minn. and the R398 adhesive manufactured by Ciba GiegyCorporation, Ardsley, N.Y. Because the high shear strength, highfracture toughness adhesive does not serve as an elastic foundationsupport for the fibers of the composite, it is not necessary that theadhesive have matrix reinforcing properties. Thus, any adhesive havingpeel and sheer strengths comparable to FM 300, AF147 or R398 may beemployed. The chosen adhesive must, of course, be compatible with thebase resin in terms of service temperature, require life, etc. as wellas have the properties discussed above.

While preferred embodiments of the invention have been illustrated anddescribed, it will be appreciated that various changes can be madetherein without departing from the spirit and scope of the invention.Consequently, the invention can be practiced otherwise than asspecifically described herein.

The embodiments of the invention in which an exclusive property orprivilege is claimed are defined as follows:
 1. A method of making adelamination resistant fiber reinforced resin composite comprising thesteps of:forming a fiber reinforced resin composite panel from aplurality of plies and a resin matrix; forming a fiber reinforced resincomposite reinforcing member from a plurality of plies and a resinmatrix; and, bonding said fiber reinforced resin composite panel to saidfiber reinforced resin composite reinforcing member with a high shearstrength, high toughness, thermosetting resin adhesive layer, saidthermosetting resin being different from the resin used to form saidresin matrix of said fiber reinforced resin composite panel and saidfiber reinforced resin composite reinforcing member.
 2. The methodclaimed in claim 1, wherein the resin used to form said fiber reinforcedresin composite panel is cured prior to said fiber reinforced resincomposite panel being bonded to said fiber reinforced resin compositereinforcing element by said high shear strength, high toughness,thermosetting resin adhesive layer.
 3. The method claimed in claim 2,wherein the resin used to form said fiber reinforced resin compositereinforcing member is cured prior to said panel being bonded to saidfiber reinforced resin composite reinforcing member by said high shearstrength, high toughness, thermosetting resin adhesive layer.
 4. Themethod claimed in claim 1, wherein the resin used to form said fiberreinforced resin composite reinforcing member is cured prior to saidpanel being bonded to said fiber reinforced resin composite reinforcingmember by said high shear strength, high toughness, thermosetting resinadhesive layer.
 5. The method claimed in claim 1, wherein the resin usedto form said fiber reinforced resin composite panel, the resin used toform said fiber reinforced resin composite reinforcing member and saidhigh shear strength, high toughness, thermosetting resin adhesive layerare all cured simultaneously.
 6. The method claimed in claim 1,including the step of crossply stitching the plies of said fiberreinforced resin composite panel to enhance the delamination resistanceof said fiber reinforced resin composite panel.
 7. The method claimed inclaim 6, wherein the resin used to form said fiber reinforced resincomposite panel is cured prior to said fiber reinforced resin compositepanel being bonded to said fiber reinforced resin composite reinforcingelement by said high shear strength, high toughness, thermosetting resinadhesive layer.
 8. The method claimed in claim 7, wherein the resin usedto form said fiber reinforced resin composite reinforcing member iscured prior to said panel being bonded to said fiber reinforced resincomposite reinforcing member by said high shear strength, hightoughness, thermosetting resin adhesive layer.
 9. The method claimed inclaim 6, wherein the resin used to form said fiber reinforced resincomposite reinforcing member is cured prior to said panel being bondedto said fiber reinforced resin composite reinforcing member by said highshear strength, high toughness, thermosetting resin adhesive layer. 10.The method claimed in claim 6, wherein the resin used to form said fiberreinforced resin composite panel, the resin used to form said fiberreinforced resin composite reinforcing member and said high shearstrength, high toughness, thermosetting resin adhesive layer are allcured simultaneously.
 11. The method claimed in claim 6, including thestep of crossply stitching the plies of said fiber reinforced resincomposite reinforcing member in order to enhance the delaminationresistance of said fiber reinforced resin composite reinforcing member.12. The method claimed in claim 11, wherein the resin used to form saidfiber reinforced resin composite panel is cured prior to said fiberreinforced resin composite panel being bonded to said fiber reinforcedresin composite reinforcing element by said high shear strength, hightoughness, thermosetting resin adhesive layer.
 13. The method claimed inclaim 12, wherein the resin used to form said fiber reinforced resincomposite reinforcing member is cured prior to said panel being bondedto said fiber reinforced resin composite reinforcing member by said highshear strength, high toughness, thermosetting resin adhesive layer. 14.The method claimed in claim 11, wherein the resin used to form saidfiber reinforced resin composite reinforcing member is cured prior tosaid panel being bonded to said fiber reinforced resin compositereinforcing member by said high shear strength, high toughness,thermosetting resin adhesive layer.
 15. The method claimed in claim 11,wherein the resin used to form said fiber reinforced resin compositepanel, the resin used to form said fiber reinforced resin compositereinforcing member and said high shear strength, high toughness,thermosetting resin adhesive layer are all cured simultaneously.
 16. Themethod claimed in claim 1, wherein said fiber reinforced resin compositereinforcing member is formed of at least two elements, said two elementsbeing juxtaposed along at least one surface and including a further highshear strength, high toughness, thermosetting resin adhesive layerlocated between said juxtaposed surfaces for attaching said juxtaposedsurfaces together.
 17. The method claimed in claim 16, wherein the resinused to form said fiber reinforced resin composite panel is cured priorto said fiber reinforced resin composite panel being bonded to saidfiber reinforced resin composite reinforcing element by said high shearstrength, high toughness, thermosetting resin adhesive layer.
 18. Themethod claimed in claim 17, wherein the resins used to form said atleast two elements used to form said fiber reinforced resin compositereinforcing member are cured prior to said elements being bondedtogether and to said panel by said high shear strength, high toughness,thermosetting resin adhesive layers.
 19. The method claimed in claim 16,wherein the resins used to form said at least two elements used to formsaid fiber reinforced resin composite reinforcing member are cured priorto said elements being bonded together and to said panel by said highshear strength, high toughness, thermosetting resin adhesive layers. 20.The method claimed in claim 16, wherein the resin used to form saidfiber reinforced resin composite panel, the resin used to form said atleast two elements used to form said fiber reinforced resin compositereinforcing member and said high shear strength, high toughness,thermosetting resin adhesive layers are all cured simultaneously. 21.The method claimed in claim 16, including the step of cross-plystitching the plies of said fiber reinforced resin composite panel toenhance the delamination resistance of said fiber reinforced resincomposite panel.
 22. The method claimed in claim 21, wherein the resinused to form said fiber reinforced resin composite panel is cured priorto said fiber reinforced resin composite panel being bonded to saidfiber reinforced resin composite reinforcing element by said high shearstrength, high toughness, thermosetting resin adhesive layer.
 23. Themethod claimed in claim 22, wherein the resins used to form said atleast two elements used to form said fiber reinforced resin compositereinforcing member are cured prior to said elements being bondedtogether and to said panel by said high shear strength, high toughness,thermosetting resin adhesive layers.
 24. The method claimed in claim 21,wherein the resins used to form said at least two elements used to formsaid fiber reinforced resin composite reinforcing member are cured priorto said elements being bonded together and to said panel by said highshear strength, high toughness, thermosetting resin adhesive layers. 25.The method claimed in claim 21, wherein the resin used to form saidfiber reinforced resin composite panel, the resin used to form said atleast two elements used to form said fiber reinforced resin compositereinforcing member and said high shear strength, high toughness,thermosetting resin adhesive layers are all cured simultaneously. 26.The method claimed in claim 21, including the step of cross-plystitching the plies of said at least two elements used to form saidfiber reinforced resin composite reinforcing member in order to enhancethe delamination resistance of said elements.
 27. The method claimed inclaim 26, wherein the resin used to form said fiber reinforced resincomposite panel is cured prior to said fiber reinforced resin compositepanel being bonded to said fiber reinforced resin composite reinforcingelement by said high shear strength, high toughness, thermosetting resinadhesive layer.
 28. The method claimed in claim 27, wherein the resinsused to form said at least two elements used to form said fiberreinforced resin composite reinforcing member are cured prior to saidelements being bonded together and to said panel by said high shearstrength, high toughness, thermosetting resin adhesive layers.
 29. Themethod claimed in claim 26, wherein the resins used to form said atleast two elements used to form said fiber reinforced resin compositereinforcing member are cured prior to said elements being bondedtogether and to said panel by said high shear strength, high toughness,thermosetting resin adhesive layers.
 30. The method claimed in claim 26,wherein the resin used to form said fiber reinforced resin compositepanel, the resin used to form said at least two elements used to formsaid fiber reinforced resin composite reinforcing member and said highshear strength, high toughness, thermosetting resin adhesive layers areall cured simultaneously.